Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $175.26   10.446%   $193.5677   $193.57   $193.55   $193.60  
  Purchase #2 $182.67   13.209%   $206.7989   $206.80   $206.80   $206.80  
  Purchase #3 $135.55   4.872%   $142.154   $142.15   $142.15   $142.20  
  Purchase #4 $58.56   5.290%   $61.6578   $61.66   $61.65   $61.70  
  Purchase #5 $95.78   13.150%   $108.3751   $108.38   $108.40   $108.40  
  Purchase #6 $11.96   3.693%   $12.4017   $12.40   $12.40   $12.40  
  Purchase #7 $250.39   7.638%   $269.5148   $269.51   $269.50   $269.50  
  7 purchase totals = $910.17       $994.4700   $994.47   $994.45   $994.60